82 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



was rather resistant against the burning effect of the spray materials. 

 Twigs bearing from 20 to 30 leaves were employed. 



The spray was applied to the foliage by means of a large atomizer 

 of the type in which quart jars are used as a container for the liquid. 

 The twigs were sprayed until the leaves began to drip, approaching 

 as nearly as possible the conditions of field spraying operations. 

 Each sprayed twig was then placed in a jelly glass of water, the 

 stem extending through a hole punched in the tin cover. (See Plate 

 XI, figs. 1,2.) 



After the spray had thoroughly dried, allowing from 6 to 12 hours, 

 20 insects were placed on the leaves of each twig. A large paper 

 bag was then placed over the twig and held to the glass by means of a 

 rubber band. (See Plate XI, fig. 1, at right.) 



Observations were usually made every other day; in some cases 

 every day. At each examination the bag was removed and the dead 

 larvae taken out and counted. When all the insects were dead, or 

 had pupated, as the case might be, the amount of foliage consumed 

 was measured in square inches. A sheet of celluloid cross-sectioned 

 to one one-hundredth of a square inch was utilized for this purpose. 

 These measurements were easily taken, where effective poisons 

 were used, as the young larvae died before very much foliage had 

 been consumed. The younger larvae ate only one surface of the leaf, 

 but as they increased in size the leaves were often skeletonized. 

 Owing to this fact it became necessary to differentiate between the 

 one and two surface feedings. Therefore, in order to equalize these 

 conditions, the measurements of the one surface feeding were divided 

 by two. Another difficulty in securing feeding measurements in the 

 case of unsprayed twigs used as checks was encountered when the 

 entire leaf, except the midrib and larger veins, was consumed. In 

 such instances the outline of the leaf was nearly obliterated, thus 

 rendering actual measurements in the ordinary way impossible. 

 However, since the leaves of the wild cherry selected for the experi- 

 ments were fairly uniform in size, this difficulty was overcome by 

 taking the measurement of an average-size leaf and substituting it 

 for the leaf the outline of which had been destroyed. This method 

 gave approximately accurate results. Careful attention was given 

 to the condition of the foliage throughout the experiments so as to 

 supply the larvae with palatable food at all times. It was seldom 

 necessary, however, to renew the foliage, except for the unsprayed 

 lots, which were quickly devoured. 



Commercial lime-sulphur testing 33° Baume was used at strengths 

 varying from J-50 to 6-50. * In lots 4 and 5 of Table VI home- 

 boiled lime-sulphur testing 30° Baume was used at the rate of 1^-50. 



i All the strengths indicated as above signify a given quantity of poison diluted with water to make a 

 total of 50 gallons of spray material. For example, lime-sulphur, 1^-50, means H gallons concentrated 

 lime-sulphur solution diluted with water to make 50 gallons of spray material. Arsenate of lead, 2-50, 

 means 2 pounds arsenate of lead diluted with water to make 50 gallons of spray material. 



